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Is this cylinder head toast? Damaged helicoil.

  • Thread starter Thread starter MechMessiah
  • Start date Start date
M

MechMessiah

Guest
I finally got the cylinder head off my bike (it's got some snapped bolts) and once I got it inside and cleaned up a bit, I discovered that one of the bolt holes had already been fitted with a helicoil from a prior owner. Well the threading in the cylinder head for the helicoil is stripped and I'm wondering if it can be repaired or not. There isn't much area left if this would need to be re-drilled.

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It can be fixed. Heads are cheap, depending on which model it's for. Could go either way. That's just a valve cover bolt, it shouldn't get torqued very tight anyway, although your PO obviously didn't know that. The other bolts were probably tightened just as tight, are those threads damaged too?

Looks like it's already off the engine so it's just as easy to go either way.

Which model is it?
 
That is not a helicoil, but one of the "better" more aggressive solutions. IMHO You would not have hard the problem with a helicoil.
 
A machine shop can install a solid bushing and then drill and tap it. Easy job but not sure how much it would cost.
 
FIRST thing, are you sure it was a Helicoil, & not just the aluminum threads that came out? This happens often when people don't use the CORRECT torque wrenches to install cam caps.
Ray.
 
I just got off the phone with a local machine shop and he confirmed it is not a helicoil, just a threaded insert. And he also suggested it would be cheaper to just get a replacement rather than having it worked on. The bike is a 82 gs650g, and yes the head is already off the bike. I don't think any of the other free threads are damaged but it does have 5 snapped bolts in addition to this, so 6 issues total.
 
Too late now but one key thing during engine disassembly is avoiding broken bolts. If you use penetrating spray like PB Blaster, along with heat from a propane torch, you will greatly reduce the risk of broken bolts. Also, never force any screws. Get a short handled ratchet or use a 1/4" drive jobby. Work the screw back and forth, both directions, until you can get it to crack loose. Once that happens it will allow a path inside the threads for more PB Blaster. Work slow, don't force anything, and 90% of the time you can get the screw out without damage.

Removing broken screws isn't overly difficult but it is very fiddly. You gotta grind the nub flat and then center punch the center of the screw. Then use left hand drill bits, starting with a small pilot screw in the center of the old screw. After the first pilot hole you need to then slowly step up in bit size and make sure you work the hole into the center of the busted screw. By the time you get near the screw diameter the nub will spin out from the drill bit torque. All pretty easy stuff as long as you can keep the bit centered and don't get in a rush.

Regarding that damaged insert, I'd get a new one of the same size and use some Loctite stud and bearing locker and set the new insert into the head with that. The valve cover only needs a light torque so the insert should stay in place as long as you don't over torque the screw.
 
Nessism said:
Regarding that damaged insert, I'd get a new one of the same size and use some Loctite stud and bearing locker and set the new insert into the head with that. The valve cover only needs a light torque so the insert should stay in place as long as you don't over torque the screw.
Click to expand...

The threading in the head is stripped out. You can drop the insert in the hole and pull it out again with a little back and forth wiggling. The hole has to be retapped and with the snapped bolts I'm not sure if I can manage all this with hand tools. I live in a second floor apt and do all my repair work on the street. So it looks like I'll be hitting up ebay and the local salvage place.
 
with the torque value as low as it is on the head cover, i would be tempted to use some good ol' jb weld on that. jb a helicoil in the hole, let it cure with the cover in place and a bolt in it to position it, i betcha it would work well enough, and cheaper than a new head. what've you got to lose.....not like it will grenade if it doesnt work....
 
If you read thread #6 you will see that he has 5 other bolts broken off in the head that need repaired also :)
 
Looking at the bosses on the other side and the length of the insert that came out is it possible to just drill the hole a little deeper, tap it and use a longer stock size bolt or install an insert far down the hole? Anybody else done this or know if those bosses are solid all the way to the bottom? I think they are.
 
zuzu said:
If you read thread #6 you will see that he has 5 other bolts broken off in the head that need repaired also :)
Click to expand...
Yup, this thing is all jacked up. Even if I get the snapped bolts and stripped threading figured out it's still gonna need to have the valves cleaned and thoroughly looked over. One particular valve set has this very sandy like build up.

Sandy said:
Looking at the bosses on the other side and the length of the insert that came out is it possible to just drill the hole a little deeper, tap it and use a longer stock size bolt or install an insert far down the hole? Anybody else done this or know if those bosses are solid all the way to the bottom? I think they are.
Click to expand...
Now that could work. There is a lot more material/space on the lower part of the head and I could use the JB weld as a gap filler for the excess room. Thanks!
 
Well none of the local machine shops wanna touch this thing, the local salvage place has no 650 heads, and the propane torch, vice grips, BP blaster method is yielding no result. Ebay here I come.
 
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